1. Field of the Invention
The present invention relates to computer controlled sprinkler irrigation systems.
2. Description of the Prior Art
In general there are two types of sprinkler irrigation. One type is the moving type which is characterized by a continuous operation of a sprinkler head or heads while a movement of the head or heads over the field to be irrigated takes place. The other type is the set type which is characterized by a multiplicity of sprinkler heads mounted in fixed positions throughout the field to be irrigated. The usual set system involves a number of sprinkler heads whose combined capacity greatly exceeds the capacity of the water source. Consequently, in order to operate the sprinkler heads near capacity they are grouped together into a plurality of zones each of which is communicated with the water source while the other zones are turned off. Systems of this type are particularly desirable in irrigating relatively large lawn areas, golf courses, athletic fields, relatively small agricultural fields and the like.
Set systems while obviating the problems incident to moving a sprinkler head or heads while in continuous operation, present the corollary problem of turning on and turning off the various sprinkler zones. A further advantage of set systems is that since each sprinkler head always operates in the same area, it can be sized to accommodate the particular area. Consequently, there remains only one major variable to choose properly in order to achieve the greatest efficiency in the use of the water applied; namely, the time each sprinkler head or sprinkler zone is operated.
It has long been the practice in set systems to use automatic controllers to turn the various sprinkler zones on and off. In general, it can be stated that the prior art controllers have viewed the turn on-turn off procedure simply as a matter of time. Often toward the end of the operation time, the area receiving the water is incapable of receiving any more water resulting in inefficient run off. Examples of typical controllers are found in the following U.S. Pat. Nos.: 3,114,243, 3,123,304, 3,723,753, 4,007,458, 4,061,927, 4,165,532 and 4,189,776.
In general it can be stated that in all of the typical controllers noted above, the operator must select the operating times for each sprinkler zone and feed these actual times into the controller so that the system will be controlled in accordance with the times selected. Whether or not the most efficient times have been selected becomes a matter of trial and error. The problem presented is that the most efficient sprinkling times can vary depending upon various conditions which may change from season to season.
In some of the earlier proposed systems, e.g. U.S. Pat. Nos. 2,578,981 and 2,674,490, a soil moisture sensor was employed to initiate a program. However, the program is a fixed routine that continues independent of soil conditions until the program is completed. It has also been proposed in U.S. Pat. No. 3,037,704 to control the length of an irrigation period based on feedback from a soil moisture sensor. Beyond these early simplistic proposals, there has been only one proposal in the patented literature to utilize a computer capability in the controller to compute an irrigation program based upon more than one single simplistic sensor input.
U.S. Pat. No. 4,015,366 to Hall is directed to a computer controlled agricultural production system. One portion of the overall system relates to a computer controlled irrigation system. The computer monitors soil moisture content by means of a soil moisture sensor. When the computer determines that the soil moisture content is approaching the minimum desirable value, the computer will determine whether irrigation is necessary in view of meteorological data and evapotranspiration data. Assuming that no rain is expected, the computer will then calculate the amount of water needed to bring the water level in the soil to an optimum level.
The Hall patent teaches that the computer may also control the speed of a pump employed with the sprinkling system in accordance with the water absorption rate characteristics of the soil being irrigated. Reference is made in the Hall patent to Jensen et al, "Scheduling Irrigation Using Climate-Crop-Soil Data," Journal of the Irrigation and Drainage Division, I.R.I., March 1970, pages 25 et seq. and Jensen, "Scheduling Irrigations With Computer," Journal of Soil and Water Conservation, Vol. 25, No. 5, September/October 1969, pages 193 et seq. as teaching the use of a programmed computer to determine the amount of water and the rate of applications.
While the computer system of U.S. Pat. No. 4,015,366 deals with more than one variable in order to achieve efficiency, namely water needed and pump speed or application rate, variation of the application rate of the system by varying the pump speed is an expensive proposition. Moreover, it is inapplicable to many systems such as those sometimes utilized in lawns, golf courses and athletic fields where the source of water utilized is the city main. Thus, in systems of this type where high efficiency is at a premium, application rate is constant and cannot be varied. There still exists a need for a computerized system which will secure maximum efficiency based upon plural variables without utilizing application rate as one of the variables.